src/mb/pcengines/apu2/mainboard.c: Fix retrieving serial number
Handle situation when first NIC is not BDF 1:0.0. The PCI enumeration
is different when a external PCIe device is connected to mPCIe2 slot
which is routed to first PCIe bridge. The first NIC is then assigned
BDF 2:0.0, because it is connected to the second PCIe bridge.
Read the secondary bus number from the NIC PCIe bridge before attempting
to read MAC adress and calculating serial number.
Change-Id: I9f89a6f3cd0c23a2d2924e587338f69c260b12f8
Signed-off-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Reviewed-on: https://review.coreboot.org/c/29842
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>